Twin rotor compressor with mating external teeth



TWIN ROTOR'COMPRESSOR WITH MATING EXTERNAL TEETH Filed Nov. 23, 1962 May 11, 1965 J. R. THORSON 5 Sheets-Sheet 1 May 11, 1965 J. R. THORSON 3,132,900

TWIN ROTOR COMPRESSOR WITH MATING EXTERNAL TEETH Filed Nov. 23. 1962 v 5 Sheets-Sheet 2 y 1965. J- R. THORSON 3,182,900

TWIN ROTOR COMPRESSOR WITH MATING EXTERNAL TEETH 5 Sheets-Sheet 3 Filed NOV. 23. 1962 INVENTOR. Jasw 7/30/5250 12mg? HTTOIFNE) y 1, 1965 J. R. THORSON 3,182,900

TWIN ROTOR COMPRESSOR WITH MATING EXTERNAL TEETH Filed NOV. 23, 1962 5 Sheets-Sheet 4 INVENTOR I? T'Iamso/v y 1955 J. R. THORSOIN 3,182,900

TWIN ROTOR COMPRESSOR WITH MATING EXTERNAL TEETH Filed Nov. '23, 1962 5 Sheets-Sheet 5 :iTgEJ INVENTOR. \Ehw f2 Fromm/v HTTORIVEYJ 3,182,900 TWIN ROTOR COMPRESSOR WITH MATING EXTERNAL TEETH John R. Tho'rson, Columbus, Ohio, assignor, by mesne assignments, to Davey Compressor Company, Kent, Ohio, a corporation of Ohio Filed Nov.'23, 19 62, Ser. No. 239,450

11 Claims. (Cl. 230-141) This invention relates to improvements in rotary compressors or motors with mating external tooth rotors.

More specifically, this invention comprises a compressor or motor composed of at least two intermeshing toothed rotors whose tooth profiles are in conjugate continuous contact, revolving within a close fitting casing having end plates, having porting means for supplying fluid at or near working chambers of maximum volume in the case of a compressor and porting means for discharging compressed gases at or near the working chambers of minimum volume; the porting means being reversed, of course, in .thecase of a motor. Therotors of this invention are constructed so that the teeth tips are on a plane which passes through their respective rotor axes, and the rotors have mutually coacting teeth which maintain lines or surfaces of sealing tooth-to-tooth, and tooth-to-housing, so that in the case of a compressor, internal preliminary compression occurs in the working chambers of decreasing volume between the casing and rotor teeth, and final compression occurs between continuous contacting teeth contours of the mating rotors as the working chambers reduce to a minimumor negligible volume at a timed or valved discharge. In a specific form of this invention, the coacting rotors have parallel axes and the rotors in intermeshing position have tooth profiles engaging each other and the casing at least in plural line contacts at all times during their intermeshing relationship, these line contacts being parallel to the rotor axes and the line contacts between a given pair of intermeshing teeth moving progressively between one position of this pair of teeth near the periphery of one of the rotors, and a second or minimum 'volume position adjacent the root circle of the same rotor and the discharge port means communicating in turn with each of the working chambers in its minimum volume position in the case of a compressor or the inlet port means communicating with each chamber in its minimum volume position in the case of a motor.

One of the features of this invention is the fact that during the final compressing-action, in the case of a compressor for air or gases, the compressing action is substantially radial of the coacting rotors.

Other objects and advantages of this invention will be apparent from the accompanying description and drawings and the essential features will beset forth in the appended claims.

In the drawings, 7

FIG. 1 is a central sectional view through one embodiment of this invention for utilization as a compressor;

FIGS. 2 and 2A are sectional views taken along similarly numbered lines of FIG. I, the coacting positions of the rotors being different in the two views;

FIG. 3 is an end view of the similar compressor but provided with different discharge port means;-

FIG. 4 is a fragmental sectional view of the same taken along the line 4-4 of FIG. 3; while FIGS. 5 through 8 are diagrammatic views showing other coacting rotor teeth adapted to carry out this invention.

One form of air compressor currently widely used utilizes mating rotors or impeller of helix shape. One advantage of this type of compressor is that it is capable of operating at high speed but various forms of this com- United Patent Patented Ma 11,1965

pressor have disadvantages such as a large unexhausted clearance volume at the point of discharge or a long seal line between the helical rotors or leakage areas during the compression cycle reducing the efficiency of the apparatus. Also, in this type of screw compressor the volumetric change depends upon the length of the helix and the wrap angle. The present invention is capable of use at high speed and avoids these difficulties encountered with the machines having helical rotors. 7

While this invention may be utilized either as a compressor or a motor, a presently contemplated use of the 11 and 12. Those familiar with this art will understand 3 that where compressive action takes place betweenthet rotors and the casing, the clearance between the rotors' and the generally cylindrical casing walls and the casing end plates is of the order of a few thousandths of an inch. This is sufiicient to provide efficient compressor action together with the structure about to be described, but the sealing action may be improved between the rotors and the end plates by sealing strips in a known manner. Also, the sealing action between the rotors and the barrel portion of the casing may be improved, and other advantages achieved, by the provision of an oil fog within the casing as is commonly done.

The rotors about to be described are dissimilar as to shape and dissimilar as to the numbers of intermeshing tooth profiles although it will be later described how these relationships may be similar in both cases.

Refer-ring first to the male rotor 13, it is tightly fitted on a central shaft or arbor 15 which is accurately and rotatably mounted in the end plates by means of bearings 16 and 17. To the left of the end plate 11, as seen in FIG. 1, a flywheel 18 is tightly secured to the'shaft 15 for rotation therewith. This flywheel is provided with a protective housing 19 secured to the end plate 11 in any suitable manner (not shown). Where-the shaft 15 extends outside of the casing and housing there are provided suitable seals 20 and 21. One of the rotors must be driven from a power source and in this case a drive shaft 22 is keyed into the hollow end shaft 15 and extends to the left beyond-the housing 19 as seen in FIG. 1 for attachment to any suitable power source.

The gate rotor 14 is rotatably mounted in the end" plates by bearings 23 and 24. This rotor has a hollow central bore 14a through which extends a tubular member 25 which extends beyond the end plate 12'at the righthand side of FIG. 1 for discharge of compressed air as at 25d thus reducing friction between the rotor 14 and the tubular member 25. It should be understood that at the zone 250 there is a clearance of a .few thousandths of an inch sealed by spring pressed sealing vanes 28. Thus, there is very little friction between the rotor 14 and the member 25a the rotor travels on its bearings 23 and 24.

Means is provided to obtain a positively timed drive between the rotors 13 and 14. To this end, a pinion 29 is keyed to the shaft 15 and meshes with a gear 30 keyed to the left-hand end of rotor 14 as seen in FIG. 1. Because rotor 13 has three tooth profiles and the rotor 14 has six tooth profiles, the ratio of the pitch 3 circles of the pinion 29 and gear 30 are of the order of 1 to 2 as will be readily understood.

Referring now to FIGS. 2 and 2A, an important form of this invention is shown wherein the rotors 13 and 14 rotate on parallel axes, the rotation being in the direction of the arrows shown in the drawings. An air inlet is shown at 31 leading through the outer wall of the casing. At the left-hand side of FIGS. -2 and 2A, it will be noted that the outer peripheries of the tooth profiles of rotors 13 and 14 have a visible clearance with the walls of the casing but making contact with the walls of the casing in the position of the parts shown in FIG. 2A. Here, air is trapped in pocket 32 between rotor 14 and the casing while another pocket of air is shown at 33 between rotor 13 and the easing. In the position of the parts in FIG. 2A, tooth 13a is making line contact with tooth 14a just as these teeth pass the point a on the casing so that a chamber of preliminary compression 34 shown in FIG. 2 is established immediately following the position of the parts shown in FIG. 2A while a working chamber 35 is provided between the two coacting rotors in the position shown in FIG. 2A. At this time, one line of contact between the two rotors is established as previously mentioned at 100 and a second line of contact at 36. These two lines of contact between the tooth profiles exist between two coacting teeth at all times during their intermeshing relationship. These two lines of contact at 100 and 36 are parallel to the rotor axes and they move progressively radially inwardly of rotor 14 from the position of FIG. 2A to a position just preceding that shown in FIG. 2. During such travel of the tooth profiles toward each other, it is obvious that the trapped air in the chamber 35 is compressed and driven radially inwardly of rotor 14. Preferably the tooth profiles approach each other so closelyat the point of discharge as to leave a substantially negligible clearance volume.

To provide for the discharge of this air in the working chamber. a discharge port 37 is provided at each zone where the rotors approach each other most closely, such ports extending through the rotor 14 to the interior surface thereof and communicating with a fixed discharge port 38 extending substantially radially through the wall of the tubular member and into the hollow central portion thereof indicated at 2511 leading to an exterior point of discharge. It will be seen that the discharge of compressed air from the working chamber has just begun in FIG. 2A and has just been completed in FIG. 2.

According to the compression ratio desired, the communication between ports 37 and 38 may be established earlier or later than shown in FIGS. 2 and 2A. Specifically, these ports may be arranged to communicate after some compression has occurred in working chamber 35.

A valve arrangement is provided as ports 37 and 38 move into and out of registration. Other types of valves might be used to time the discharge of compressed air.

Various tooth profiles may be used in carrying out this invention. Referring to FIG. 2A, the portion A of the tooth of rotor 14 is an involute curve, the portion B is a circular arc, and the portion C is a trochoid. On the rotor 13, the portion A is an involute, the portion B is a circular arc, and the portion C is a cycloid. The portions B and B are arcuate about a center 39 lying on the pitch circle of the rotor 13. The portions D and D are very short cylindrical lands lying respectively on the pitch circles of the two rotors. The portions A and A are hereinafter referred to as leading profiles as they are of the first to engage. The portions C and C are hereinafter referred to as trailing profiles. The leading profiles carrying out this invention may be either cycloidal, involute, or circular arcs, or combinations of those three, or other profiles not defined by simple mathematical equations. It is essential to the operation of this compressor that there be continuous contact between these surfaces with uniform rotational speed of each rotor providing what herein has been designated as conjugate action, together with a motion, uniform or non-uniform, of the seal or contact zone toward the trailing profiles seal zone. As to the trailing profile, the only profile which will operate with the compressor being described is one which makes sealing contact first at the intersection 10a of the housing or casing and the outside or maximum diameter of the two rotors. The trailing profile here is a point-generated profile or trochoid on the gate rotor 14. The trailing profile on the rotor 13 is also point generated and thus trochoidal or cycloidal. It will be noted in the structure just described that the teeth on rotor 13 are addendum only and the teeth on rotor 14 are dedendum only.

The ports 40 are for the introduction of an oil fog as is common in rotary compressors.

FIGS. 5 through 8 show somewhat diagrammatically other cross sectional views of mating rotors adapted to carry out this invention. This showing is by no means exhaustive as many rotors may be utilized to carry out the teachings of this invention.

In FIG. 5, two identical rotors 41 and 42 shown insofar as tooth shape is involved, with equal numbers of teeth on the two rotors and with each tooth being partially addendum and partially dedendum. The leading profiles of the teeth in this example are cycloidal and there is a small cylindrical land at both the tip and the root of each lobe.

In FIG. 6, coacting rotors 43 and 44 are shown having equal numbers of teeth with rotor 43 having lobes which are addendum only and rotor 44 having lobes which are dedendum only. The leading profile in the two structures shown here are cycloidal. No land is shown at the lobe tips of rotor 43 although these could be provided if desired.

In FIG. 7, rotor 45 is shown with three lobes and rotor 46 with four. The lobes on rotor 45 are addendum only. The lobes on rotor 46 are dedendum only. Here the leading profiles on each rotor are involutes, except for the portion E which is trochoidal to prevent interference with the tips of the lobes on rotor 45.

In FIG. 8, rotor 47 has four lobes and rotor 48 has six. The lobes on rotor 47 are addendum only while the lobes on rotor 48 are dedendum only. The leading profiles in each case are circular arcs.

The operation of each form shown in FIGS. 5 through 8 is identical with that already described. Inlet air is provided at 31', the coacting rotors make sealing contact at their outside of maximum diameters, first at the point 10a on the casing, two line contacts occur between mating teeth, such contacts being parallel to the rotor axes and the line contacts between a given pair of intermeshing teeth moving progressively between one position on the pair of teeth near the periphery of the gate rotor, 42, 44, 46, 48, and another minimum volume position adjacent the root circle of the gate rotor, and the compressed air is discharged from the working chamber between intermeshing teeth through discharge passageways 37' and 38 to the hollow central passageway of a fixed tubular member 25.

Other discharge port means may be provided while utilizing the other features of this invention, that is, other than that shown in FIGS. 1, 2 and 2A. Referring now to FIGS; 3 and 4, a compressor following the teachings of this invention having rotors 50 and 51 identical in tooth profile with rotors 13 and 14 are provided in a casing 10 having an. air inlet 31" and having a point 10a" opposite the inlet 31" where the profiles of mating teeth on rotors 50 and 51 make their first sealing contact at the outside maximum diameter of each rotor as more fully set forth in the first described form of this invention. Two mating teeth are shown in dot-dash profile forming a working chamber 35 between them. It should be understood that the rotor 50 may be mounted on a fixed arbor 52 utilizing bearings in the position of bearings 23 and 24 as shown in FIG. 1. In at least one of the end plates 53, closing the casing is provided a fixed discharge port 54 at the point where the tooth profiles of the mating rotors reach a working chamber of minimum substantially negligible volume. Preferably, a port 54 is provided in an end plate opposite the plate 53 shown in FIG. 4. Near the root of each tooth profile on rotor 50, there is provided a discharge passageway 55 and preferably each of these tapers from a position of minimum depth at the center line 56 of the rotor 50 toward a position of maximum depth at each end plate 53 opposite the discharge'port 54. As seen in the dot-dash position of the teeth in FIG. 3, each working chamber 35 may discharge through the passageways 55 to a discharge port 54 as the working chamber 35' reaches a position of minimum volume. Other than as just described, the form of compressor shown in FIGS. 3 and 4 operates like that shown in FIGS. 1, 2 and 2A.

In each case where I have used the word contact describing engagement between teeth of mating rotors, or between the teeth of rotors and the casing walls, I intend the word to mean in both specification and claims, an approach within a few thousandths of an inch such that under working conditions, the leakage is such as to provide a commercially acceptable performance.

If desired, means may be provided for draining oil from the compressor housing, a longitudinally extending groove being shown in the bottom of the housing 10.

What is claimed is:

1. In a rotary compressor, a casing having body walls and end Walls, a pair of rotors rotatably mounted in said casing on parallel axes and closely fitting said end walls and having intermeshing axially straight tooth profiles cooperating with each other and with the casing walls to form preliminary compression pockets and final compression working chambers varying during rotor rotation between positions of maximum and minimum volume to compress a fluid between them, there being inlet and outlet port means associated with said casing, each of said preliminary compression pockets communicating with said inlet port means prior to compressive action, each of said working chambers in its position of minimum volume having means communicating with said outlet port means, said rotors having compressive engagement with said casing walls and with each other to form said preliminary compression pockets in which compression takes place during rotor rotation, said rotors having coacting tooth profiles first mutually engaging in at least line contact for intermeshing action near the outer peripheries of said rotors at a zone where said rotors leave a common Zone of casing contact between them, said rotor intermeshing tooth profiles simultaneously engaging in at least line con-tact at a second zone circumferentially spaced from said first named zone, said linecontacts being parallel to said rotor axes, and said line contacts between each coacting pair of intermeshing teeth moving progressively toward the root circle of one of said rotors completing said compression of trapped fluid to said minimum volume position of said working chamber.

2. The combination of claim 1 wherein said intermeshing tooth profiles cause internal compression within each working chamber prior to establishment of communication through said outlet port means.

3. A compressor as defined in claim 1 wherein one only of said rotors is provided with outlet port means communicating exteriorly of said casing at the zone where said rotors approach each other most closely, and the other rotor at said zone having tooth lobe profiles which substantially completely fill the intertooth space of said one rotor adjacent the root circle of the latter, whereby the intertooth spaces of both of said rotors are fully used.

4. A compressor as defined in claim 3 wherein driving means including a shaft integral with said other rotor is connected to said other rotor only, intermeshing timing gears on said two rotors drive said one rotor in timed relation to said other rotor, whereby'said driving means can carry said other rotor as an integral part, and hearing means for said shaft and for said other rotor in the end walls of said casing.

5. In a rotary compressor, a casing having body walls and end walls, a pair of rotors rotatably mounted in said casing on parallel axes and closely fitting said end walls and having intermeshing axially straight tooth profiles cooperating with each other and with the casing walls to form preliminary compression pockets and final'compression working chambers varying during rotor rotation between positions of maximum and minimum volume, means for simultaneously rotating said rotors, there being inlet port means associated with said casing and communicating with the intertooth spaces of said rotors; there being outlet port means associated with one only of said rotors at the zone where said rotors approach each other most closely and communicating exteriorly of said casing, the intertooth spaces of said rotors communicating with each other to form said preliminary compression pocketsas coacting teeth on said rotors approach each other during rotation, the tips of said coacting teeth substantially sealing against said casing and closing said pockets, said coacting rotor teeth tips simultaneously leaving a common zone of easing contact and conjugately establishing a moving seal with each other there and at the same time forming said working chambers by establishing a second conjugate seal at a zone arcuately spaced from said first named conjugate seal, both of said conjugate seals being spaced radially outwardly from the root circle of said one rotor, and thereafter during rotor rotation said conjugate seals approaching each other and approaching the root circle of said one rotor until the space between said rotors is negligible where said rotors approach each other most closely, said seals between said teeth tips and said casing and said conjugate seals all being parallel to said rotor axes.

6. In a machine having a pair of rotors with axially straight intermeshing teeth for use with compressible fluids, a casing having body walls and end walls, said pair of rotors rotatably mounted in said casing on parallel axes and closely fitting said end walls, said rotors during rotation having successive pairs of intermeshing teeth and pairs of adjacent teeth forming with said casing successive chambers of varying volume; at maximum volume a chamber being defined by sealing contact between profiles of intermeshing teeth and by contact of adjacent teeth with said body walls of said casing, said intertooth spaces on the two rotors between said intermeshing teeth and said adjacent teeth then communicating; at an intermediate volume said chamber being defined by circumferentially spaced sealing contacts between intermeshing teeth; at minimum volume said chamber being defined by substantially a merging of said spaced sealingcontacts between intermeshing teeth; said rotors and easing being so constructed and arranged that said change between that position of teeth, one on each rotor, in contact with said casing body walls and that position of the same teeth in mutual sealing contact occurs almost simultaneously; there being high pressure fluid port means communicating successively with said chambers only at said minimum volume position thereof, and there being low pressure fluid port means communicating successively with said chambers at said maximum volume position thereof; whereby upon rotation in one direction fluid introduced at said high pressure fluid port means and discharged at said lower pressure fluid port means will drive said machine as a motor, and driving said rotors in the opposite direction while introducing fluid at said lower pressure fluid port means and discharging said fluid at said high pressure fluid port means will cause said machine to act as a compressor.

7. A machine as defined in claim 6, wherein one of said rotors is a gate rotor in which rotor only said high pressure fluid port means is provided communicating at the root diameter with each of the tooth spaces of said gate rotor. Y

8. A machine as defined in claim 7 wherein said gate rotor is rotatably mounted on an axially extending hollow shaft having a port communicating with said high pressure fluid port means and with a point exterior of said casing. 9. A machine as defined in claim 7 wherein port means is provided through at least one of said end walls of said casing and communicating with said high pressure fluid port means.

10. A machine as defined in claim 6 wherein the sealing contacting profiles of said rotors are mutually generated, whereby said sealing contact is maintained between the tecth--oljd rotors through said minimum and maximum and intermediatevolume positions of said chambers. 11. A rotary compressor for compressive fluid having a pair of intermeshed tooth rotors and comprising:

(a) a casing; (12) an inlet port in said casing for compressive fluids; (c) a primary rotor in said casing having a plurality of axially straight teeth and rotating about a first axis; (d) a stationary hollow shaft in said casing having its axis parallel to said first axis;

(e) a gate rotor having a plurality of axially straight teeth and rotatably mounted on said hollow shaft, said gate rotor intermeshing with said primary rotor during rotation, said rotors being so constructed and arranged that (i) the surface of a tooth of said primary rotor establishes a first sealing contact with the surface of a coacting tooth of said gate rotor while the following tooth of each rotor engages said casing thus merging a tooth space of each rotor into a single compression chamber bounded by the surfaces of both said rotors and by said casing,

(ii) on continued rotation said compression chamber being reduced in size until the tooth tip of said primary rotor establishes a second sealing contact with said gate rotor circumferentially spaced from said first sealing contact, said compression chamber then bounded by the surfaces of said primary rotor and of said gate rotor,

(iii) on continued rotation said compression chamber being further reduced in size to a minimum volume where said first and second sealing contacts merge,

(iv) on continued rotation said sealing contact is broken opposite said inlet port and the tooth spaces separate, having been replenished with fluid from said inlet port, and

. (v) on continued rotation the fluid in the tooth spaces is trapped between the rotors and said casing as the tips of said teeth contact the surfaces of said casing,

(f) a communication passage between each tooth on said gate rotor passing from the outer surface of said rotor to the surface of said hollow shaft;

(g) a discharge port through said hollow shaft positioned to index with said communication passage when each said compression chamber is at minimum volume, thereby allowing the compressed fluid to be discharged.

References Cited by the Examiner UNITED STATES PATENTS 883,894 4/08 Knowles 230-141 1,418,741 6/22 Stallman 103-126 1,728,528 9/29 Butler 103-126 1,728,529 9/29 Butler 103-126 1,902,346 3/33 Vogt 103-126 2,400,485 5/46 Cardillo 103-126 FOREIGN PATENTS 1,029,201 4/58 Germany.

JOSEPH H. BRANSON, JR., Primary Examiner.

40 WILBUR J. GOODLIN, Examiner. 

1. IN A ROTARY COMPRESSOR, A CASING HAVING BODY WALLS AND END WALLS, A PAIR OF ROTORS ROTATABLY MOUNTED IN SAID CASING ON PARALLEL AXES AND CLOSELY FITTING SAID END WALLS AND HAVING INTERMESHING AXIALLY STRAIGHT TOOTH PROFILES COOPERATING WITH EACH OTHER AND WITH THE CASING WALLS TO FORM PRELIMINARY COMPRESSION POCKETS AND FINAL COMPRESSION WORKING CHAMBERS VARYING DURING ROTOR ROTATION BETWEEN POSITIONS OF MAXIMUM AND MINIMUM VOLUME TO COMPRESS A FLUID BETWEEN THEM, THERE BEING INLET AND OUTLET PORT MEANS ASSOCIATED WITH SAID CASING, EACH OF SAID PRELIMINARY COMPRESSION POCKETS COMMUNICATING WITH SAID INLET PORT MEANS PRIOR TO COMPRESSIVE ACTION, EACH OF SAID WORKING CHAMBERS IN ITS POSITION OF MINIMUM VOLUME HAVING MEANS COMMUNICATING WITH SAID OUTLET PORT MEANS, SAID ROTORS HAVING COMPRESSIVE ENGAGEMENT WITH SAID CASING WALLS AND WITH EACH OTHER TO FORM SAID PRELIMINARY COMPRESSION POCKETS IN WHICH COMPRESSION TAKES PLACE DURING ROTOR ROTATION, SAID ROTORS HAVING COACTING TOOTH PROFILES FIRST MUTUALLY ENGAGING IN AT LEAST LINE CONTACT FOR INTERMESHING ACTION NEAR THE OUTER PERIPHERIES OF SAID ROTORS AT A ZONE WHERE SAID ROTORS LEAVE A COMMON ZONE OF CASING CONTACT BETWEEN THEM, SAID ROTOR INTERMESHING TOOTH A PROFILES SIMULTANEOUSLY ENGAGING IN AT LEAST LINE CONTACT AT A SECOND ZONE CIRCUMFERENTIALLY SPACED FROM SAID FIRST NAMED ZONE, SAID LINE CONTACTS BEING PARALLEL TO SAID ROTOR AXES, AND SAID LINE CONTACTS BETWEEN EACH COACTING PAIR OF INTERMESHING TEETH MOVING PROGRESSIVELY TOWARD THE ROOT CIRCLE OF ONE OF SAID ROTORS COMPLETING SAID COMPRESSION OF TRAPPED FLUID TO SAID MINIMUM VOLUME POSITION OF SAID WORKING CHAMBER. 